1. Field of the Invention
This invention relates in general to machinery for boring holes in the earth. In particular, the invention relates to a earth boring tool for attachment to a prime mover such as a backhoe.
2. Description of Related Art
Earth boring rotary tools have been in use for many years. However, there still remains room for improvement. Many tools are too large or too complicated to be easily attached to a prime mover, such as a backhoe. Also, many tools have the thrust offset from the center of rotation, which causes cocking.
Some prior art tools have had a three part piston rod, with a center portion defining a rod chamber for accommodating a drive shaft as the piston moves upward. Problems arose when the rod chamber decreased in volume, thus greatly increasing the pressure in the rod chamber. These highly increased pressures have caused hydraulic leaks and, in some cases, catastrophic failures.
A need existed for an earth boring rotary tool having some apparatus for relieving the fluid pressure in the rod chamber. Also, the tool needed to have the thrust concentric with the center of rotation to prevent cocking. In addition, the tool needed to be easily adaptable to various uses.